The Thermal Protection System (TPS) of spacecraft is an important development of the National Aeronautics and Space Administration (NASA). Broadly, the TPS of a spacecraft includes the various materials, manufacturing methods, design details, testing techniques and procedures of installation developed to protect the space shuttle vehicle from the severe temperature and heat transfer environments encountered in the various phases of each shuttle mission. A TPS typically includes three subsystems, a Reusable Surface Insulation Subsystem (RSISS), a Leading Edge Structural Subsystem (LESS) and a Penetration Subsystem (PSS). The RSISS constitutes most of the TPS and typically consists of flexible blankets and rigid ceramic-like tiles, plus the assembly concepts used to put the system together. The nature of the tiles make them extremely resistant to heat, but also brittle and susceptible to damage from structure-induced loads. Further, the tiles must be attached in a way capable of accommodating some level of error in alignment. That is, if tiles are slightly misaligned, they must not be attached in a way that pushes adjacent tiles into one another to the point that they are structurally unsound. Accordingly, tile-to-structure attaching systems have been developed that isolate the delicate tiles from damaging structure-induced loads.
Current tile-to-structure attaching systems include adhesive and mechanical methods of tile attachment. While existing adhesive methods provide for a strong and flexible bond to the structure, they do not allow for convenient removal and reattachment of the tiles. Tiles in areas that require frequent access to the structure of the aircraft or spacecraft are therefore made with a hole in the center of the tile allowing for placement of a metal fastener from outside the aircraft or spacecraft to affix the removable tile to the structure. A densified ceramic plug of refractory material similar to that of the tile is then used to plug the gap between the top of the metal fastener and the outer surface of the tiles. In this fastening arrangement, an internally threaded receptacle is placed inside an oversized hole of a densified ceramic plug made of refractory material similar to that of the tile. A close-cut disk is then inserted on top of the plug and the assembly is bonded to a mating hole in the tile using an adhesive. The resulting receptacle floats in the tile and can accommodate lateral misalignment of about 0.03 in. (0.076 cm.) and azimuthal misalignment of a few degrees.
While mechanical attachment systems allow for rapid attachment and removal of insulating tiles, they still require an assembly to be adhesively bonded to a mating hole in the tile. These inserts are further complicated in that they require attachment to special hard points within the sandwich structure of the vehicle.